Plasma shield may stun and disorientate enemies

The US Army hopes, within a few years, to deploy a plasma shield - a machine that generates a protective screen of dazzling mid-air explosions - to stun and disorient an enemy.

The device uses a technology known as dynamic pulse detonation (DPD). A short but intense laser pulse creates a ball of plasma, and a second laser pulse generates a supersonic shockwave within the plasma to generate a bright flash and a loud bang.

The Plasma Acoustic Shield System will eventually combine a dynamic pulse detonation laser with a high power speaker for hailing or warning, and a dazzler light source. PASS has already been demonstrated by the system's makers, Stellar Photonics.

"It uses a programmed pattern of rapid plasma events to create a sort of wall of bright lights and reports (bangs) over the coverage area," says Keith Braun of the US Army's Advanced Energy Armaments Systems Division at Picatinny Arsenal in New Jersey, US, where the system is being tested.

Force delivery

Braun puts the maximum range of the system at around a hundred metres. But he says the PASS laser is unlikely to be used as a weapon, in its current format, since it lacks sufficient power. Unlike other high-power lasers which burn a target, the DPD relies on a shockwave. Braun says it would take several minutes to burn through a piece of paper using the laser.

"It is fair to say that any stunning or disabling of a target individual would require additional force on target," says Braun. "The current state-of-the-art in portable, rugged laser systems is not at the point of sufficient power."

However, he does not rule out the possibility altogether: "This type of capability is at the core of what we eventually expect from the technology."

Indeed, PASS may be the first step towards a man-portable, tuneable laser weapon that could be used in both non-lethal and lethal modes. Stellar Photonics, which has a $2.7 million contract to build PASS , plans to develop smaller and more powerful versions in future.

Speed of light

The company has also pitched a portable laser rifle, which would be lethal, to the US Army. It would weigh about fifteen kilograms, would have a range of more than a mile, and could have numerous advantages over existing rifles - better accuracy and the ability to hit a moving target at the speed of light.

It could also be used in non-lethal mode, "offering the individual soldier a first response non-lethal alternative, with the capability to go lethal should the situation call for that level of response", says Braun. But extensive testing of its effects on humans would need to be carried out before it could be legitimately used as a non-lethal weapon.

Some other high-energy laser systems, like the Airborne Laser (a missile defence system being developed by Boeing) rely on large chemical lasers, firing a continuous beam, and the chemicals used are both toxic and corrosive. PASS will use a solid-state laser, which only needs a supply of electricity, but the engineering challenges are still significant, says Braun.

"The biggest problems with mobile laser systems in the field are the power supply concerns, overall size of the laser and optics, and the tolerance for those optics to endure rapid changes in temperature, airborne particulate and the kinds of vibrations a military platform imparts on its load." Says Braun.

The PASS laser is due to be tested in 2008, with testing of the full prototype PASS turret on a vehicle in 2009.

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